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Thursday, October 9, 2014

Given the recent FCC Report & Order on U-NII (Unlicensed National Information Infrastructure) rule changes in March/April of 2014, I thought it would be helpful to recap the new regulations in the United States regarding the 5 GHz unlicensed spectrum bands. I've put together the following table for quick reference:

Additionally, here is a graphic of the 5 GHz U-NII bands, both current and proposed, from the NTIA report made in January 2013 (note - this graphic does NOT reflect the change with regards to the extension of U-NII 3 up to 5.850 GHz).

Saturday, September 27, 2014

I previously posted a picture of an SNR to MCS data rate mapping table that I have compiled based on various sources of credible research. Keith Parsons has kindly put this information into a printable format for reference. You can download them below.

It should be noted that individual devices perform differently. These tables are simply generic estimates that are a good approximation for many Wi-Fi devices. In other words, it's not perfect.

This table maps client SNR values to MCS indexes for the purpose of determining the data rates that clients can achieve based on the signal quality of their connection to the AP.

SNR is also related to RSSI. Two RSSI values are of importance: the Minimum Receiver Sensitivity and the Expected Receiver Sensitivity. The 802.11 minimum receiver sensitivity tables often referenced in research and testing material are the required minimum RSSI values that a radio should be able to decode a given modulation type and encoding rate (MCS index) with a packet error rate (PER) less than 10%. Most 802.11 radios provide better receiver sensitivity than the minimum requirement. Therefore, the "Expected Receiver Sensitivity" reflects the typical receive sensitivity of clients with the ability to achieve any given MCS index at a lower RSSI than the minimum receiver sensitivity required to pass testing. For example, the minimum receiver sensitivity for an 802.11ac 20 MHz PPDU at MCS 9 is -57dBm, but most 802.11ac radios can decode this PPDU at a lower RSSI such as -62dBm.

It should also be noted that a receiver's ability to perform Maximal Ratio Combining (MRC) across multiple receive antenna chains is not reflected in this SNR chart. MRC can allow a device to receive the incoming signal at a lower energy level at each of the individual antenna inputs to the RF front-end radio circuitry which are then combined using digital signal processing (DSP) to provide additive gain. This effectively increases the SNR the client experiences. MRC is based on each client device's receive antenna chain specifications and the number of spatial streams being used for the link between the client and AP, with extra receive radio chains being used for MRC. After MRC gain is added, you can use this table to lookup the MCS rate the client may be able to achieve given it's final resulting SNR . Also be aware that many manufacturer receive sensitivity specifications will list RSSI and SNR values 3-6 dB lower than what is specified here because they list the signal level at the antenna input prior to DSP and MRC gain.

Some of the references used to help compile this table (not an exhaustive list):

Thursday, August 21, 2014

I've been thinking of writing a well-articulated blog post on why the preference for high-density Wi-Fi networks is smaller channel width over larger channel width. This post is NOT that.

Instead, I was on Twitter articulating some of the logical points why smaller channel widths provide better aggregate capacity than larger channel widths (assuming you deploy enough radios and take advantage of all the spectrum at your disposal). Here is a quick recap of those points.

You might want to reference my SNR to MCS Index Mapping Table, which shows why larger channels result in a reduction in modulation rate that can often offset the gain from using the wider bandwidth in the first place. And my 802.11ac Receiver Sensitivity charts show that you have to have a really great signal strength for wider channels to even be considered, but watch out in your design because overcompensating to achieve higher signal strength will increase co-channel interference (CCI) which travels a LONG ways! Finally, my post on 802.11ac Adjacent Channel Interference (ACI) shows that wider channels create more ACI than smaller channels, and ACI is even more detrimental and unfriendly than CCI. Therefore, radio receivers require greater adjacent channel rejection (up to 8dB more), and with fewer channels for frequency re-use ACI is more likely.

Wednesday, August 20, 2014

Following my previous post regarding typical SNR to MCS rate mappings for Wi-Fi clients, an interesting discussion was held on Twitter regarding the effects of increased channel width on the ability of a client to decode frames at any given SNR. Long story short, wider channels increase the noise power captured by the receiving radio which reduces its SNR. For every doubling of channel width, you require 3dB better signal to achieve the same MCS rate.

George Ou created a chart showing the relative range of each MCS rate based at various channel widths:

Following up on his work, I thought it would be useful to provide some context around these coverage ranges by referencing it against a typical noise floor of -93 dBm found in many environments. Using this noise floor and the SNR to MCS rate mapping table, combined with the relative coverage ranges (based on RF signal propagation using the inverse square law) we can visualize what data rates a typical 802.11ac radio will experience at various RSSI and SNR signal levels for each channel width.

Note - these receiver sensitivities are not absolute. Wi-Fi radios vary. But this chart is a good approximation for many radios and provides a generic reference for you to visualize and understand this effect.

Tuesday, August 19, 2014

If a Wi-Fi station has a better signal, you get more throughput. Everyone knows that. Here is a handy chart to help visualize it.

This table shows the "typical" data rates that Wi-Fi stations can achieve based on their SNR (signal to noise ratio). I say "typical" because it actually varies based on the radio chipset receiver sensitivity, but these values are a good starting point for most devices.

The achievable data rate (MCS rate) varies based on a number of variables:

The 802.11 protocol - really a function of the increasing maturity of chipsets over time to handle more complex modulation types even when SNR is a bit lower.

The channel width - typically doubling the channel width increases the noise floor by 3 dB, which decreases SNR. So to get the same MCS rate on wider channels you need higher SNR.

The complexity of the modulation - notice as you get into more complex modulations like 64-QAM and 256-QAM that it doesn't take much more SNR to move from the lower encoding rate to the higher encoding rate, and vice versa in the opposite direction.

Saturday, August 16, 2014

In the Cisco landscape today, there are three features that usually come up in the same conversation. They all solve what I'd call "related" problems, but are not the same. They are incredibly useful features and do share one thing in common...you must know your RF environment before implementing them. I'll provide use-cases and examples below, but it should be noted that in the case of "Optimized Roaming", this is based on public information currently available and could change prior to the WLC AirOS version 8.0 release.

Optimized Roaming

The problem:

The well known "sticky client" issue. For the uninitiated, when a client refuses to roam to an assumedly "better" AP (closer, stronger RSSI, better SNR etc.) that client is being "sticky". Why is this bad? Consider the following example of a lecture hall:

As the client enters the room, it associates to AP-1. As it moves farther away from AP-1 it's RSSI gets weaker, SNR gets worse, retransmissions occur, dynamic rate-shifting happens, and you end up with a client communicating at a much lower data-rate. Lower data-rate consumes more air-time to transfer the same information, resulting in higher channel utilization. Ideally, the client would roam to AP-3 and the resulting RF space would be better for everyone.

The Solution:

With Optimized Roaming, once the client reaches either a certain RSSI, Data-Rate, or both, the AP will send an 802.11 Disassociation Frame. Ideally, after receiving a disassociation frame, the client will then associate to the closer AP (AP-3 in our example). The RSSI is from the perspective of the AP. Both RSSI & Data-rate are configurable.

If the situation were reversed and our client is leaving the building, optimized roaming can also help. If this same client, or even a less "sticky" one, were to exit the building it may still be at or around -81 for quite some time. Considering that AP-5 is in a lobby, next to glass doors, it's possible for clients to remain connected as they approach a parking lot some distance away. While they hang on to their WiFi connection for dear life, it would be a far better experience for these clients if they drop off WiFi and pick up their 3G/4G connection.

Notes:

Optimized Roaming has a built-in hysteresis. This prevents "thrashing", or a client idling at or around the threshold and therefore being disassociated, re-associating, getting disassociated again, etc. By default this threshold is 6dBm. For example, if your threshold is -75, and a client gets disassociated, that client will not be able to associate (or re-associate) to that AP until it reaches at least -69. Remember, this is from the perspective of the AP.

You can use Data-rate, instead of or in addition to, RSSI. If both are configured, both must pass in order for the client to associate.

RSSI Low Check

The Problem:

In our last example, we outlined the issue of clients leaving a building but remaining on WiFi for far too long. A related issue is that of clients who are merely walking by the building, on their way to somewhere else. They never get stronger than a -80 RSSI, but their mobile device prefers WiFi over 3G/4G. The client tries to connect, sometimes succeeds sometimes fails. Either way, it's a poor connection, at best, leading to a poor user experience. I personally experience this often; consider the following example:

The main paths of this Campus have no outdoor coverage, however bleed-over from each building is enough for a Mobile device to "try".

The Solution:

With RSSI Low check enabled, a clients association requests will be ignored, unless the AP hears them stronger than -80 (configurable). To be more accurate, the 802.11 Association Request will be followed by an Association Response with status code 0x0022, meaning "poor conditions". Attached is a .pcap of this occurring (with a threshold of -60 set). Here is what it looks like:

The takeaway here is that you do not need RSSI Low Check, if you are using Optimized Roaming. Reason being: a client must pass the Data RSSI value, configured for Optimized Roaming, in order to associate. Therefore, Optimized roaming is really a replacement for, and better than, RSSI Low Check. Thankfully, it's also configurable in an RF Profile.

Why would you use RSSI Low Check? Well, for one, RSSI Low Check is available today. At the time of this writing Optimized Roaming is not (WLC 8.0 code). Secondly, I've personally not tested Optimized Roaming in a full production environment with thousands of client-types. It's possible that certain clients, upon receiving a disassociation frame, will not immediately rejoin the ESS leading to "client issues". I think that second possibility will be rare, but possible.

Notes:

If, for some reason you have both Low Check & Optimized Roaming configured, both must pass in order for a client to associate. For example, if Low RSSI Check is set to -65 and Optimized Roaming is set to -75, the client must be at -65 or stronger to associate.

Receive Start of Packet (RX-SOP)

This is arguably the coolest of the three, and surprisingly, has been around the longest. In it's first form (7.2 code I believe) it was hidden. It was then unhidden (7.5 I believe) and finally with 8.0 will be part of the GUI. You can't find any reference to RX-SOP that doesn't also include something along the lines of "if you use this, beware, it may destroy you". I can understand Cisco's trepidation about releasing this to the populous. It is powerful. It is dangerous. Remember that sentence before about knowing your RF environment? Ok disclaimer over. I'd highly recommend you go read the NSA Show review of RX-SOP, by @samuel_clements and @blakekrone. They did a great job with it, including experiments & graphs.

The Problem:

High Co-channel contention & channel utilization in high-capacity environments. The rules of co-channel interference should always be followed (avoid it!), but in HD environments it is sometimes unavoidable. What results, is typically a situation where an AP is holding off transmitting to it's clients, due to CSMA/CA. More specifically, the CCA-Carrier Sense will kick off at anything above -85 for a STA (AP or Client), and the medium determined 'busy' for the time specified by the Length value of the SIG field in the PLCP Header. Further, CCA-Energy Detect will determine the medium 'busy' at anything 20dBm stronger (-65). I'm skipping over Virtual Carrier Sense (NAV) and sticking to just the PHY for this discussion. For description of both Physical & Virtual mechanisms of CSMA/CA check here, here, here or here.

Consider the following crude drawing:

This presents a situation where AP-1 "could" successfully transmit to Client-1, assuming sufficient SINR, but it does not, due to CSMA/CA.

The Solution:

RX-SOP essentially takes any frame received below the set threshold and dumps it in the Noise bucket. It's been described as tuning the AP Receive Sensitivity, or applying "Ear Muffs". Taking our example, if RX-SOP is configured at -80, AP-1 does not "hold-off", because it doesn't determine the medium as "busy" due to AP-2's transmissions. As far as AP-1 is concerned, the Medium is free to use (all be it, a bit more noisy). You can see how this could greatly improve performance in the Downlink direction.

Notes:

Client behavior does not change. If a client determines the medium busy, with or without RX-SOP yields the same result (it will back-off). In other words, this does not improve the Uplink direction.

If you configure just RX-SOP, without Optimized Roaming, it is possible that a "sticky client" will fail hard. If the client does nothing (but retransmit), in the absence of any ACK's, it could take a while for it to roam. Probably not a common occurrence, but possible.

The success of RX-SOP is dependent on SINR. Your environment will determine whether, or how much, RX-SOP will help and what level it should be set to.
I can only speculate on exactly how RX-SOP is implemented. Does the determination happen at CCA-CS; the receipt of the Short Training Field (STF) in the Preamble, or is it after receiving the full PLCP Header? Or is it happening before that? Not sure, but it's been a tool in the bag for quite some time. Check the further reading section for more.

Monday, August 4, 2014

I was reading this article on development of 5G cellular technologies when this bit on OFDM deficiencies and the need for new waveforms to support higher capacities and user densities caught my attention (emphasis added by me):

4G and 4G+ networks employ a type of waveform called orthogonal frequency division multiplexing (OFDM) as the fundamental element in the physical layer (PHY). In fact, almost all modern communication networks are built on OFDM because OFDM improved data rates and network reliability significantly by taking advantage of multi-path a common artifact of wireless transmissions. However as time and demands progress, OFDM technology suffers from out-of-band spectrum regrowth resulting in high side lobes that limit spectral efficiency. In other words, network operators cannot efficiently use their available spectrum because two users on adjacent channels would interfere with one another. OFDM also suffers from high peak-to-average ratio of the power amplifier, resulting in lower battery life of the mobile device. To address OFDM deficiencies, researchers are investigating alternative methods including generalized frequency division multiplexing, filter bank multi-carrier, and universal filter multi-carrier. Researchers speculate that using one of these approaches over OFDM may improve network capacity by 30 percent or more while improving the battery life for all mobile devices."

This aligns with most Wi-Fi professionals' recommendations to deploy 5 GHz radios on non-adjacent channels to avoid that dreaded adjacent channel interference (ACI).

And if you look at an OFDM Wi-Fi transmit spectral mask, either the limits defined in the standard or using a spectrum analyzer, you will see rather significant side lobes that can impact adjacent channels (and channels even further away, depending on proximity and power levels). I have even considered including discussion of OFDM spectral masks within my 802.11ac presentations and writing due to the fact that as channel widths get wider, so to do their side lobes because the frequency distance from the main carrier signal at which the relative power level must be reduced to be in compliance increases as well. Here is an illustration that I put together over a year ago but never published and kept in the appendix of my 11ac presentation. It illustrates how ACI can increase due to the spectral mask differences as channel widths get larger. I have inlaid two 20 MHz spectral masks inside the 40 MHz mask, and two 40 MHz masks inside the 80 MHz mask. Essentially, the side lobe power level reduction requirements are based on the size of the main signal lobe; as the main signal lobe gets larger, so too does the allowed power in side band lobes.

Spectral Mask Comparison of 20, 40, and 80 MHz Wi-Fi Channels

And below is a capture from a spectrum analyzer approximately 10 feet away from an 802.11ac AP operating in 80 MHz mode with a large amount of traffic. Notice the high signal level in adjacent channels (52-64, and likely would impact the as-of-yet unapproved U-NII 2B band).

Spectrum Analysis Capture of an 802.11ac 80 MHz Waveform

This is why you need a minimum of 10 feet of separation between radios operating in the same frequency band (unless other shielding mechanisms are used, which increase cost), as well as the recommendation to have adjacent 5 GHz radios operating on non-adjacent channels. This will start to become a bigger issue as we deploy more 5 GHz radios to handle capacity and user density demands. More manufacturers are considering developing software-defined radios (SDR) as well as multi-radio APs that have more than one radio operating in the 5 GHz band. You should carefully research and verify (through real-world testing) these solutions to ensure that interference within the AP is not an issue.As always, the better you understand what's going on at the physical layer, the better wireless engineer and architect you will be.

Friday, April 11, 2014

According to a new report completed by Telecom Advisory Services, LLC (Raul Katz, Columbia Business School) commissioned by WiFiForward, the economic value of unlicensed spectrum is over $228 Billion per-year in the U.S. alone!

The Report Overview (1 page) highlights the use-cases and value of each. WiFiForward has also produced an infographic (shown at right) to highlight the various ways in which unlicensed spectrum provides economic value in the U.S.

The report details the value of unlicensed spectrum in the U.S. based on two different economic impacts:

Gross Domestic Product (GDP) - direct sales of technologies, services and applications that run on unlicensed spectrum. This results in $6.7 Billion per-year in value ($4.559 Billion of which is attributed to Wi-Fi).

Economic Surplus - use of technologies that rely on unlicensed spectrum that add value to the economy. This results in $222 Billion per-year in economic value ($91.474 Billion of which is attributed to Wi-Fi).

Missing Data?
I am a bit confused since the value from enterprise Wi-Fi sales and resulting efficiencies appears to be absent from this analysis. Worldwide sales of enterprise Wi-Fi equipment alone is over $4.4 Billion annually according to IDC. A significant portion of that market is in the U.S. but does not appear to be included in the GDP figures from this report, which only include the value from Wi-Fi cellular offloading, WISPs, and wireless PANs (BT, ZigBee, WirelessHART). Additionally, no economic surplus value is attributed to efficiencies that enterprises gain from private Wi-Fi deployments. Surely there is a tremendous amount of cost savings that organizations realize through the use of Wi-Fi that has not been captured in this report!

Just as a quick point of comparison to licensed cellular wireless sales and services, which have been reported as $225 Billion in wireless wide area network (WWAN) sales (including mobile handsets) as of 2006 (Reference The Case for Liberal Spectrum Licenses (Hazlett & Leo, 2010), pg.15). And since the ARPU of mobile network operators is shifting to data-driven pricing, and Wi-Fi offload represents over 50% of mobile data traffic, a case could be made that over half of the mobile handset sales should be attributed to Wi-Fi / unlicensed spectrum instead.

And comparing the data-carriage portion of the WWAN industry to the Wi-Fi offload value, Benkler writes (pg. 98):

Mark Cooper of Consumer Federation of America offers a more expansive approach that includes both imputed value of unlicensed bundled as part of cellular service and savings from Wi-Fi offloading on the supply side and arrives at about $50 billion per year.And in light of efforts to quantify specifically the data-carriage side of Verizon and AT&T’s business that suggest a revenue more on the order of $50 to $55 billion per year for licensed mobile data in the United States,Hazlett and Leo’s claim of a vast disparity in value appears to be inflated.

So what can we conclude in comparison? The total value of licensed versus unlicensed is very similar, at both an aggregate level and a mobile data traffic handling level, even without reapportioning a significant percentage mobile handsets sales to Wi-Fi.

Comparison to Previous Research
The full report describes the methodology used for arriving at these figures and provides and extensive comparison of the current work with prior research on this topic. It is quite an interesting read! A few of the previous studies and reports on the value of unlicensed spectrum include those listed below.

Note - many of these studies use older statistics for the basis of the figures, which are no longer accurate. These include Wi-Fi penetration in consumer households, the percentage of Wi-Fi traffic offloaded from cellular networks, and mobile handset Wi-Fi penetration.

2009 - The economic value generated by current and future allocations of unlicensed spectrum (Thanki)
- Value of Wi-Fi in consumer homes in the U.S. is $4.3 - $12.6 Billion per-year based on broadband extension over Wi-Fi, and also increases broadband adoption creating an additional $5.2 - $15 Billion per-year in economic surplus (based on 2006 figures, pg. 27).
- The total value of three unlicensed uses-cases (Wi-Fi in homes, Wi-Fi in hospitals, and RFID) is $16 - $37 Billion per-year in the U.S. (Note: Thanki cautions that these figures are likely significant underestimates on the value of unlicensed spectrum because they only account for 15% of the total unlicensed chipset market.)
- Potential value created by unlicensed / Wi-Fi uses of white spaces could be $3.9 - $7.3 Billion per-year.
- Potential for new unlicensed uses of white spaces for rural broadband and agriculture water savings could be $0.8 - $4.3 Billion per-year in the U.S.

I've read through the R&O, and here are the technical modifications that were approved:

U-NII 1 band (5.150 - 5.250 GHz) indoor operation restriction is removed. This allows use of the band for outdoor hotspots, WISPs, and bridge links. The growth of public hotspots will clearly benefit from this change.

AP power levels at the Intentional Radiator may be 1W (previously 50mW) and the EIRP may be 4W using a 6dBi antenna (previously 200mW), and following the 1dB reduction rule in transmitter power for every 1dB of antenna gain above 6dBi.

Client power levels at the IR may be 250mW and the EIRP may be 1W, following the 1:1 dB reduction rule for antenna gain above 6dBi.

WISPs may use up to 23dBi antennas on fixed point-to-point links without any corresponding reduction in transmitter power.

These changes help to unify the U-NII 1 band with the U-NII 2A/2C and U-NII 3 bands so that larger contiguous swaths of spectrum can be combined using 802.11ac, which provides for 160 MHz channels comprised of two 80 MHz channels. In addition, by adopting power levels commensurate with U-NII 3, 80 MHz channels that are not adjacent to one another can easily be combined as well to form a 160 MHz channel. This ultimately provides greater flexibility in combing U-NII 1 with other U-NII 2A/2C/3 channels. The higher power limits also benefit WISPs for use on point-to-point links with higher gain antennas to achieve greater distances and throughput.

In the [2013] NPRM, the Commission envisioned that harmonizing the power and use conditions across the lower 200 megahertz of U-NII spectrum (U-NII-1 and U-NII-2A) would likely permit the introduction of a wide-range of new broadband products capable of operating at higher data rates than is now possible.

Globalstar MSS is the only user of this band in the U.S., using it for terrestrial gateway uplink transmissions to the Internet and phone networks (other spectrum bands are used for the satellite spot-beam transmissions, namely the Lower Big LEO and Upper Big LEO bands). Globalstar initially objected to the U-NII 1 outdoor use and higher power level changes. However, the NCTA analysis found little risk of interference if any one of these three conditions are met:
1.) Outdoor APs do not radiate more than 125mW (21dBm) EIRP at elevation angles above 30 degrees
2.) The device is used for a Point-to-Point link
3.) The device operates indoors

Devices that do not meet one of those three conditions are limited to 250mW conducted power. Additionally, before deploying an aggregate total of 1,000 APs or more outdoors in U-NII 1, companies must report to the FCC, which will facilitate corrective measures if harmful interference does occur. This is due to the fact that all U-NII 1 devices deployed outdoors in the U.S. will contribute to the noise level of the Globalstar MSS.

U-NII 3 band (5.725 - 5.825 GHz) is expanded up to 5.850 GHz, adding 25 MHz of bandwidth that now fall under the FCC Part 15.407 rules for U-NII (effectively consolidating FCC Part 15.247 into 15.407). This means that Wi-Fi channel 165 (5825 MHz) now falls under the U-NII 3 band rules instead of the ISM rules. Hopefully this will also mean more consistent support for channel 165 in vendor implementations (it's been spotty thus far). This additional 25 MHz provides for 1 additional 20 MHz channel (165) but no additional 40, 80, or 160 MHz channel capacity. You may want to revisit my post on 802.11ac Channel Planning.

Other technical changes to the U-NII 3 band include:

PSD changes from 17dBm/MHz to 30dBm/500KHz.

No power reduction for antennas above 23dBi on fixed point-to-point systems. This should benefit outdoor WISPs and other point-to-point deployments. (Note - all non-PtP systems still require a 1dB reduction in power for every 1dB antenna gain over 6dBi).

The FCC also rejected ARRL proposed changes that would have required DFS operation from 5.65 - 5.925 GHz (including U-NII 3 and the proposed U-NII 4 band), citing no demonstrated need and that it would be overly burdensome.

Channel 165 is now part of UNII-3 (FCC Part 15.407), not ISM (FCC Part 15.247)

All devices (AP or client) operating in any U-NII band must be secured to prevent unauthorized software modification and to ensure it operates as approved to prevent harmful interference. The exact methods used to secure the software are left to the manufacturer, but must be documented in their application for equipment authorization to the FCC. The FCC is not setting specific technical security requirements since they are likely to change over time, but rather defining the capabilities that should be implemented by manufacturers. They do make note that more detailed security requirements may be necessary later as software-defined radio technology develops. They also declined to implement rules that would force manufacturers to render a device inoperable if unauthorized modifications were made, citing additional complexity and costs resulting in questionable benefits above the software security being mandated.

All documented instances of harmful interference were found to be by devices certified for operation in the U-NII 3 band which had been manipulated through software controls to operate in the U-NII 2C band and interfered with TDWR (Terminal Doppler Weather Radar) in the 5.60 - 5.65 GHz sub-section.

To quote from the R&O:"The primary operating condition for unlicensed devices is that the operator must accept whatever interference is received and must not cause harmful interference. Should harmful interference occur, the operator is required to immediately correct the interference problem or to cease operation."

Other uses of the 5 GHz U-NII bands are show below:

5 GHz U-NII Bands with Primary and Secondary Allocations

These FCC U-NII technical modifications are separate from another proposal currently under study by the FCC and NTIA that would add another 195 MHz of spectrum under U-NII rules in two new bands, U-NII 2B (5.350 - 5.470 GHz) and U-NII 4 (5.850 - 5.925 GHz). For further details read 'Wi-Fi May Get A Capacity Boost, Thanks to the FCC'.

DFS rules and compliance measurement procedures have been modified in the two existing U-NII 2 bands (U-NII 2A and U-NII 2C) to prevent harmful interference to TDWR and other radar systems. DFS is already required to be implemented if devices will operate in the U-NII 2 bands, but is being modified as follows:

Explicitly prohibits operators from using equipment without operational DFS in the U-NII 2 bands.

DFS must be turned on when operating devices in the U-NII 2 bands (it cannot be disabled).

Testing of DFS systems will be performed against a new radar waveform that more closely matches current TDWR systems.

Devices operating in U-NII 2 bands must now perform DFS radar sensing across 100% of the device emissions bandwidth (instead of 80% as specified in the 2006 DFS Compliance Measurement Procedures, Table 4). This will make DFS detection more stringent, but possibly also more prone to false-positives when radar is adjacent to the device's operating frequency range.

The DFS sensing threshold is modified. For devices operating below 200mW EIRP, the EIRP power spectral density (PSD) must now also be below 10mW/MHz in order to use the relaxed sensing threshold of -62 dBm. In practice this shouldn't cause any DFS change for most indoor Wi-Fi operation where AP power output is typically 100mW or less and EIRP is 200mW or less when using a 3dBi antenna. The minimum Wi-Fi channel width is 20 MHz, thus the 10mW/MHz PSD should be the peak limit, and larger channel widths will have even lower PSD. If operating APs at power levels above 100mW or with higher gain antennas above 3dBi then DFS sensing of radar at the lower threshold of -64dBm may come into play which could result in a slightly higher chance of detecting radar.

DFS devices no longer have to conform to a "Uniform Channel Spreading" requirement, which was intended to avoid dense clusters of devices operating on the same channel and might increase the risk of interference to radar systems. In fact, the FCC R&O acknowledges that the use of wide channels with an overall reduced number of usable channels can result in more effective spectrum use at a given location. Larger channels also spread the power of signals out uniformly over the frequency band in which the device is operating, rather than concentrated in a narrow bandwidth. This is not news to any Wi-Fi professional familiar with spread spectrum concepts :)

By removing this requirement, they also acknowledge that dynamic or manual channel selection may be used. Previously, some manufacturers accomplished channel spreading by forcing dynamic channel selection. This should no longer be the case with such products, and manual selection of U-NII 2 channels should be available in all products moving forward.

The "Channel Loading" DFS compliance measurement test no longer requires the use of an MPEG video at 30fps, citing the need for greater flexibility to test and certify devices that are not designed or capable of streaming video. Instead, channel-loading tests will be performed with data types representative of the device under test. This should open up the use of U-NII 2 bands to more devices.

The TDWR frequency range of 5.60-5.65 GHz is now available for use by U-NII 2C devices again as long as they meet all new and modified rules! For Wi-Fi networks, this means we will gain access to channels 120-128 again. This adds back to the usable inventory: three 20 MHz channels, two 40 MHz channels, one 80 MHz channel, and one 160 MHz channel. This should be of significant benefit in enterprise environments, providing another 80 MHz channel (6 total now) with Wave-1 802.11ac equipment for channel re-use planning!

We will have to wait to see the effect these DFS rule changes have on the usability of the U-NII 2 bands in practice. Many users already shy away from using DFS channels due to the risk of Wi-Fi channel change and instability in the network. I fear this will heighten apprehension and further constrain use of these bands by network operators.

DFS Radar Detection (Sensing) Thresholds

Other DFS modifications were not implemented:

The FCC declined to adopt a geo-location database requirement to lookup TDWR in the 5.60 - 5.65 GHz band. They believe the updated DFS rules are sufficient.

The FCC declined to modify the out-of-band emissions limits for U-NII devices, as their field investigations have not found properly functioning equipment with the current limits to be a problem. Again, the majority of cases were from devices operating in frequency bands which they were not certified to begin with, or devices which had DFS disabled.

All of the new rules are subject to the following transition period before they take effect:

12 months after the effective date of the R&O, applications for certification of 5 GHz devices must meet the new and modified rules.

Existing devices that do not meet the new and modified rules must cease to be manufactured, marketed or sold in the U.S. 2 years after the effective date of the R&O.

Existing devices that operate in U-NII 2 bands must always comply with DFS. If DFS is not implemented or is disabled, the devices may be confiscated.

Wednesday, April 2, 2014

Sometimes we fall into bad habits. Unfortunately, the improper use of terminology is quite common in the Wi-Fi industry. This can cause a great deal of confusion when people discuss technical topics. Therefore, as a Wi-Fi industry, I think we should start referring to the following terms using more accurate terminology so we are all on the same page.

Here goes:

Over-the-Air Rogue APs - if it's not on your wired network, it's NOT a "Rogue AP" so let's start calling them Neighboring APs so we all know what someone is talking about rather than having to inquire each and every time someone mentions a rogue for clarification. And let's reserve using the term Rogue APs for when unauthorized APs are on the internal wired network.Correct Term: Neighboring APs

Co-Channel Interference (CCI) - APs and clients that are operating on the same channel don't cause interference with one another, they contend for the same airtime and backoff if another one is transmitting. This is distinctly different from interference where a transmission cannot be properly decoded because the receiver can't distinguish the valid signal from noise.Correct Term: Co-Channel Contention (CCC)

Collision - okay, here is one that most of you may not have really thought deeply about. Collisions don't actually happen on wireless networks (not in the traditional wired network meaning of the term 'collision'). Instead, the receiver simply cannot properly decode a valid signal because it can't distinguish it from the surrounding noise with the precision required by the modulation used.Correct Term: Interference

Coverage Area - most Wi-Fi professionals refer to an APs coverage area as the physical area in which they intend for clients to connect to the AP, usually with an associated signal strength (such as -67dBm). However, the RF signal actually keeps going and can cause co-channel contention (see what I did there!) over a much larger area (usually out to a signal strength of around -85dBm). So, to refer to the area in which we expect clients to connect to the AP based on an RF design let's start using a different term such as Association Area and leave the term Coverage Area to refer to the area where CCC occurs.Correct Term: Association Area

AES versus TKIP - this one is easy to get wrong, even for Wi-Fi professionals! Many times we interchangeably use AES, TKIP, and WEP to refer to the encryption on the wireless network. However, in so doing we confuse encryption protocols with cipher suites. For accuracy we should always mention like for like. CCMP, TKIP and WEP are all encryption protocols that we configure for a wireless network. Each of those protocols use a cipher suite to accomplish the heavy lifting: CCMP uses AES, TKIP uses RC4, and WEP uses RC4. Thanks to George Stefanick for bringing this up.Correct Term(s): Reference protocols (CCMP, TKIP, WEP) or ciphers (AES, RC4) but don't use them interchangeably

802.1x - I see this all the time in written material to refer to the IEEE 802.1X Port Based Network Access Control. Unfortunately, it should be used with capital letter 'X' since it is a (standalone) standard, whereas lowercase letters refer to amendments to standards (see here). So, whenever you reference it use the correct capitalization (802.1X).Correct Term: 802.1X

WAP - many people use this term to refer to an access point and it's just annoying. It's just AP people. Referring to it as wireless AP (WAP) is just redundant.Correct Term: AP

Antenna Gain in Decibels (dB) - many people refer to antenna gain in dB, which is incorrect. Decibels (dB) alone is a relative measurement and requires a point of reference. Instead, you should refer to antenna gain referencing either an isotropic radiator (dBi) or less commonly referenced to a standard dipole antenna (dBd). This establishes the absolute reference point for the measurement which actually gives it meaning.Correct Term(s): dBi or dBd

802.11b 1 Mbps and 2 Mbps Data Rates - do you reference all of the lower data rates of 1, 2, 5.5, and 11 Mbps as 802.11b? If you do, you've been using this amendment name incorrectly. The original 802.11 standard (802.11-1997) defined the 1 Mbps and 2 Mbps data rates as part of the DSSS PHY, as is generally referred to as 802.11 Prime. Then in 1999, along came the 802.11b amendment which added the 5.5 Mbps and 11 Mbps data rates as part of the HR-DSSS PHY. So, to be correct, when talking about 1 Mbps and 2 Mbps data rates you should reference 802.11-Prime (not 802.11b).Correct Term: 802.11 Prime (or 802.11-1997)

5 GHz Signals Attenuate Faster than 2.4 GHz Signals - it's common for many Wi-Fi professionals and writers to state that 5 GHz signals attenuates faster than 2.4 GHz signals in order to describe the common symptom that 5 GHz has less effective coverage area. However, this too is incorrect in most circumstances. 5 GHz signals attenuate through free space at the same rate as 2.4 GHz signals according to the FSPL (free space path loss) formula; it is not directly dependent on the frequency of the signal. Instead, the construction of the receiving antenna is a fractional multiple of the frequency to which it is tuned. This makes a standard 1/4 wavelength antenna for 2.4 GHz longer than a 1/4 wavelength antenna for 5 GHz, which causes a difference in antenna aperture. To put it simply, a 2.4 GHz antenna has a larger aperture than a similar 5 GHz antenna and can "capture" more of the signal as it passes by the antenna element.Correct Term: 5 GHz Antennas Have Smaller Apertures

Do you have any other terms that are misleading or misused and you think should be corrected? Drop a comment below!

Monday, March 31, 2014

The FCC just made an unofficial news release of pending action that was approved at today's commission hearing which eases restrictions on the existing 5 GHz UNII-1 frequency band (5.150-5.250 GHz, Wi-Fi channels 36-48).

To quote from the news release (emphasis added by me):

By its action the Commission significantly increased the utility of the 100 megahertz of spectrum, and streamlined existing rules and equipment authorization procedures for devices throughout the 5 GHz band.

This ruling makes the following changes to the UNII-1 band:

Removes restriction on indoor use. Now the UNII-1 band can be used outdoors as well. This will allow use of the band by WISPs and for outdoor hotspot deployments which are rapidly growing with the support of telecommunications and cable operators.

Increases the allowed power output. The power output had been lower in UNII-1 than other 5 GHz UNII bands due to indoor-only use (50mW IR, 200mW EIRP). Exact details of the new power limits have not been released, but it is fair to assume the UNII-1 band will have similarly capable power output as UNII-2/2e bands (250mW IR, 1W EIRP) the UNII-3 band (1W IR, 4W EIRP). (Update after reviewing Commissioner Rosenworcel's statement and Commissioner O'Rielly's statement it appears the new power limits will be higher and align with the existing UNII-3 band).

And an additional change to all UNII bands (particularly UNII-2 with DFS restrictions):

Modified equipment authorization rules that requires manufacturers to secure devices against unauthorized software changes and illegal uses. Commissioner O'Rielly's statement makes it pretty clear that this is directed toward manufacturers of outdoor WISP equipment that allowed easy circumvention of DFS radar checks that resulted in several instances of TDWR interference and forced the FCC to restrict all Wi-Fi use in the TDWR band (Wi-Fi channels 120-128 are affected). For those interested, here is a list of Enforcement Actions against TDWR interference. Notable repetitive offending manufacturers include Motorola Canopy and Ubiquity Networks equipment.

It should also be noted that the the FCC Office of Engineering and Technology (OET) analyzed the UNII-1 changes with stakeholders to come to an acceptable outcome regarding the risk to existing licensed use for Satellite Operators (Globalstar) in the 5.150-5.250 GHz band (see the U.S. Frequency Allocation table).
The aim of today's regulation changes are to streamline the rules surrounding 5 GHz UNII bands to allow easier adoption and integration of all available spectrum into devices. I would anticipate future rulings surrounding DFS bands to make further strides in this area as well, since DFS support and adoption has been lackluster to-date and a hindrance to utilizing all available unlicensed spectrum.

Keep a close eye on future FCC rulings in the 5 GHz band around the end of this year or early 2015, when an ongoing study into adding an 195 MHz spectrum to the unlicensed 5 GHz bands should be completed. You can read more about that initiative in 'Wi-Fi May Get A Capacity Boost, Thanks to the FCC'.

Thursday, March 13, 2014

Videos of presentations from the WLAN Professionals Conference that occurred Feb. 10-12th in Austin, TX have now been posted by Keith Parsons and the Prime Image Media team. The conference was chalk-full of great content, both technical and business focused, by some of the best experts in the industry!

Tuesday, February 11, 2014

I'm here at the WLAN Professionals Conference (#WLPC if you're following on Twitter). This is the first of what hopefully will turn into an annual conference dedicated to the Wi-Fi industry. But this conference is a bit different than what you might think a typical conference is. First and foremost, it's got a grassroots, peer-to-peer focus. It's engineers talking about Wi-Fi and gathering for discussion. It's not overly promoted by vendors or full of presentations with marketing drivel. Instead, it's just people who are passionate about this technology coming together to share their knowledge and experiences with each other to better everyone! What a great concept!

There are over 100+ attendees, many of whom are also presenters. I hear there was more demand than seats available, so next year Keith Parsons, organizer of the event, should have a solid baseline to grow the conference and allow more of you (the community) to attend and get involved. What's also great is that many of the presentations have been interactive, with great questions and quality discussion fostering the entire group to share information. The focus on the technology instead of the marketing that so often surrounds the technology and products in this industry. That's refreshing!

Day one of the conference was full of great content. Since there are two tracks of presentations, I can't cover all of the great presentations that occurred, but all sessions are being recorded so I plan on going back and watching the ones that I missed. Here are the highlights that stuck out from day one for me.

First up, Matthew Gast presented on 802.11ac. In typical Matthew Gast fashion, "minds were blown!" Matthew mixes the technical geeky details along with practical implications of the technology on real-world networks and the motivations that IEEE standard developers considered when drafting the protocol amendment. At one point Matthew also entered The Matrix (no not that virtual world in which machines rule mankind, rather the steering matrix for RF beamforming), but luckily spared the audience by dumbing down the mathematics for normal engineers :) Attendees also received a copy of his 802.11ac book.

Matthew Gast presents on 802.11ac

After a much needed coffee (and brain) break, Chuck Lukaszewski presented on high-density WLAN design. Chuck's presentation highlighted the method he uses to gather a Rough Order of Magnitude (ROM) to scope customer expectations and frame the design and budget early on in the process. This included understanding the associated user capacity, active user capacity, AP layout requirements, infrastructure dimensioning, and developing the ROM quote. This serves as a great starting point to ensure all parties are on the same page early on in the project and to focus more detailed activities that will follow with on-site visits such as site surveying and design.

High Density Rough Order of Magnitude (ROM) Process

Chuck then turned to RF coverage design in stadiums, detailing the mounting options available and the preferred methods his team uses in different situations to minimize co-channel interference. One point that he highlighted was music to my ears... the fact that CCA Busy is triggered by the physical preamble and PLCP header (and NOT by the ability for a receiver to decode the MAC header and read the Duration/NAV value). This impacts the distance at which an AP or client causes CCI because the preamble and PLCP header is encoded at the minimum PHY Basic rate (e.g. 1, 2, or 6 Mbps) and can be decoded at great distances! I've been explaining this to anyone who will listen for several years and it has a HUGE impact on RF network design.

Interference (CCI) goes MUCH farther than you think!

Brad Crump from CWNP discussed certifications and your career. This was one of the most engaging and useful discussions that I've had at the conference so far. Brad posed several questions to the audience about learning methods (live class, online, self study, boot camp) which prompted some passionate debate in the room. Several members of the audience were current or former instructors and had some very good information to share about how they've been able to effectively train students. Additional discussion on vendor-neutral and vendor-specific training was lively as well. Brad framed the discussion by explaining that there is a trade-off between acquiring knowledge and attaining a certification that HR managers are looking for in employee candidates. In short, HR managers are looking for "Expertise" and they often recognize vendor brand certifications like Cisco more than vendor-neutral. But Brad and team (including Julia Baldini, marketing whiz) are working to build the CWNP into a globally recognized brand! Woohoo, I wish them great success in this endeavor. I'm a big fan of CWNP content and certifications. Go get some CWNP people!

What is expertise?

Charlie Clemmer talked in the afternoon about RF in warehouse environments. Since I used to be directly responsible for managing over 3 dozen large warehouses with varying sizes and product inventory, this is a topic near and dear to my heart. Charlie shared is insights on why warehouses are not as easy as most people think. Sure, the clients typically require low bandwidth for telnet/SSH and warehouse management applications. But the environment can be extremely challenging due to legacy client compatibility issues, very high ceilings, unique freezer environments, high availability requirements, and some interesting IDF and wired network restrictions. Once again, great discussion ensued with the audience. Several seasoned wireless engineers who deal with warehouses shared their experiences and how to solve for some of the unique challenges that can be encountered. One topic of large discussion was how to cost-effectively design WLANs by performing a hybrid site survey with predictive modeling that is grounded with real-world data from on-site surveying in select sample areas of the warehouse. Otherwise, performing a full site-survey for warehouses that can be thousands or millions of square feet in size is too time consuming and expensive.

Charlie Clemmer presents on RF in warehouse environments

Finally, I'd like to give a quick shout out to all of the old friends that I've seen this week and new friends that I've met in person for the first time. These types of events are absolutely great to meet fellow peers in the industry! Also, a shout out to Prime Image Video who are recording all of the sessions and working their magic to make this content available for everyone online who couldn't attend in person. Ben and Andrea are awesome people and they are outstanding media professionals! If I haven't met you in person at the conference yet, don't be shy, come up and say 'Hi'!

Cheers,
Andrew von Nagy

P.S. If you're at the conference, I'll be speaking about capacity planning for every WLAN on Wednesday morning. I hope you'll swing on in!

Wednesday, February 5, 2014

Over the past few years I've had the opportunity to travel for work, a lot. I'm always navigating airports large and small, and trekking out and about around urban areas finding my way from airport to hotel to meeting venue or just plain exploring the local scene in my free time. I've got a bit of an "adventure seeker" flair as well, so sometimes I just head out on my own without a map, guide, or itinerary just to soak up the local culture and find the backroads that really embody the travel destination that I find myself in.

In urban areas, this invariably involves navigating the local railway or subway system. In many places all the signs are posted in both the local language as well as English, but I always try to force myself to gather the meaning of the signs without resorting to reading the English version. One sign that is almost universal among these train systems is the warning to "Mind The Gap" between the railcar and the platform. With trains barreling down the tracks at significant speeds, railway architects need to leave a buffer of space to ensure the cars don't hit the platform.

It occurs to me that with greater velocity or momentum comes the need for more flexibility in design at the sacrifice of a small amount of precision. However, there is a fine balance to this design that must be maintained. Make the gap too large and passengers are at greater risk of injury. Make the gap too small and the rail design is too inflexible, causing damages and the system ends up breaking down quickly requiring replacement.

This serves as a fairly good analogy, in my estimation, for the wireless LAN industry. The WLAN market is like the railway car, picking up velocity and traveling at a fairly fast speed down the tracks. No one can deny the pace of change in the WLAN world, where users are adopting Wi-Fi mobile devices in record-breaking numbers, the Internet of Things (IoT) is on the horizon, and businesses are finding that Wi-Fi can actually enable new services and insights that help them differentiate. Users, meanwhile, are standing on the platforms trying to hop onto this fast-moving train, all-the-while expecting an effortless and satisfactory experience that they have been accustomed to for the past decade. WLAN administrators are caught in the middle, trying to design these systems to be flexible enough to accommodate the increased velocity and change in the industry while trying to minimize the "gap" between the railway car (WLAN services) and the platform (Users). A tough job indeed!

If WLAN administrators have any hope of succeeding in minimizing the gap, they need to place proper focus on understanding market direction and be armed with the proper tools and resources to effectively design a solution that not only meets the current needs but future needs as well. With every new advancement that comes along, the industry is challenged to identify and develop tools that enable administrators to effectively design the WLAN system based on these new capabilities and changes user demand. If the gap widens too far (product advancements or user demands outpace the ability for administrators to effectively design the WLAN) then users are at risk of falling through and suffering a poor user experience and dissatisfaction.

Therefore, a constant ebb and flow exists in the industry where the gap widens as advancements are made and user demands change, only to shrink as the technology matures, deployment experiences reveal what works and what doesn't, and administrators gain the resources to design and plan for the new requirements.

One of the major "gaps" that has arisen over the course of the last several years is the overwhelming increase in demand for Wi-Fi capacity but the lack of quality resources and tools for network administrators to design for capacity requirements. Instead, WLAN admins are forced to twist RF coverage design tools into what they need using crude rule-of-thumb estimates on the number of APs per square meter / feet based on an ambiguous (at best) concept of the network type they are planning for such as data, voice, or location-services.

I say enough is enough! We need:

Solid Understanding - Administrators need to understand what factors determine capacity in a WLAN, including AP and client capabilities, applications in use on the network, and the unique mix of devices on their network.

Holistic Planning - Administrators need to fill the gaps in the WLAN design process to adequately perform capacity forecasting. This includes proper research and requirements gathering as well as integration of capacity planning alongside RF coverage planning.

Design Approach - Administrators need an approach to WLAN capacity planning is purpose-built for the job. Relying on RF coverage tools, not designed to account for user density, device capabilities, and application demands is simply not good enough.

Quality Resources - Administrators need quality tools and resources that are built specifically to aid in the task of WLAN capacity planning. The lack of quality WLAN capacity planning tools in the industry is glaringly apparent.

Do you have gaps in your WLAN design process?

I'll be speaking about WLAN capacity planning and presenting a methodology and approach that can be used for every WLAN, big or small, at the Wireless LAN Professionals Conference next week in Austin, TX. If you're attending, please join me on Wednesday, Feb. 12th at 9am CST in Ballroom B of the Hilton Austin Airport Hotel. If you are unable to attend, a recorded video of the presentation will be made available after the event.